An image forming apparatus employing an electrophotographic image forming method has long been widely known. Not only various electrophotographic black-and-white image forming apparatuses, but also, various electrophotographic full-color image forming apparatuses have been commercialized. As an image forming apparatus has come to be widely used in various fields, the level of quality at which an image forming apparatus is required to form an image is becoming higher and higher.
More specifically, it has been desired to continuously improve an image forming apparatus in terms of the level of glossiness at which it is capable of forming a print (an image). Glossiness is one of the print (image) properties which gives a print (image) an impression of higher quality. Further, one of the primary factors which affects the glossiness of a print is the smoothness of the image bearing surface of a print.
As the means for accommodating the above described need, an apparatus has been proposed, in Japanese Laid-open Patent Applications H04-216580 and H04-362679, which yields a highly glossy print (image) by using a sheet of recording medium whose surface layer (toner reception layer) is formed of a transparent resin, and embedding a toner image into the surface layer, that is, the transparent layer formed of the transparent thermoplastic resin (this type of recording medium hereafter may be referred to as resinous medium).
In this apparatus, after the formation of a toner image on the transparent resin layer, the toner image is fixed by a fixing device. Then, the transparent resin layer, and the toner image thereon, are thermally melted with the highly glossy belt of a smoothing apparatus. Thereafter, while the resinous recording medium is conveyed through the smoothing apparatus, with the transparent resin layer in contact with the highly glossy belt, the resinous medium is cooled by a cooling apparatus. Then, the resinous medium is separated from the belt. Thus, after the separation of the resinous medium from the belt, the surface of the resinous medium, which is bearing the toner image, is as smooth as the highly glossy surface of the belt. Incidentally, the reason for cooling the resinous medium before separating it from the belt is to preventing the smoothed surface of the resinous medium from being rendered uneven again, by preventing the toner and the resinous layer of the resinous medium from offsetting onto the fixation roller.
Sometimes, it is required to produce a highly glossy two-sided print, that is, a highly glossy print having an image on both its front and back surfaces. In such cases, recording medium having a transparent resin layer on both of its two surfaces is used.
However, this method of yielding a highly glossy two-sided print by employing recording medium having a transparent resin layer on both of its surfaces sometimes suffers from the following problems:
That is, when an image is formed on both surfaces of a sheet of resinous recording medium having a transparent resinous layer on both of its surfaces, through the first step in which an image is transferred onto one (first) of the two surfaces of the resinous recording medium, fixed, and smoothed, and the second step in which another image is transferred onto the other surface (second) of the resinous recording medium, fixed, and smoothed, the smoothed first surface of the medium becomes unsmooth during the step; one of the two surfaces of the finished highly glossy two-sided print is not as glossy as desired.
This problem seems to occur for the following reason. That is, a fixing device in according with the prior art separates recording medium from the fixation belt (smoothing belt) while the recording medium is still hot; in other words, it does not allow the recording medium to cool before it separates the recording medium from the fixation belt (smoothing belt). Therefore, the smoothed first surface of the recording medium becomes unsmooth while the image on the second surface is fixed. Thus, the resultant unevenness of the first surface of the highly glossy two-sided print made with the above described two-sided resinous recording medium is more conspicuous when a fixing apparatus which is relatively high in fixation temperature is used.
Further, an image is formed on both surfaces of a two-sided resinous recording medium through the above described image formation sequence, each sheet of two-sided resinous recording medium is conveyed through the fixing apparatus—the smoothing apparatus—the fixing apparatus—the smoothing apparatus. Therefore, it is possible that the first surface, that is, the smoothed surface, of the two-sided resinous recording medium will be scarred by the pairs of conveyance rollers and pairs of conveyance guides disposed along the recording medium conveyance passage. This is another reason why the first surface side of a highly glossy two-sided print produced using an image formation method in accordance with the prior art is likely to be inferior in glossiness.